text: Diffusiophoresis is an analogous phenomenon to thermophoresis, where a species A moves in response to a temperature gradient. Both diffusiophoresis and thermophoresis are governed by Onsager reciprocal relations. Simply speaking, a gradient in any thermodynamic quantity, such as the concentration of any species, or temperature, will drive motion of all thermodynamic quantities, i.e., motion of all species present, and a temperature flux. Each gradient provides a thermodynamic force that moves the species present, and the Onsager reciprocal relations govern the relationship between the forces and the motions.
  Diffusiophoresis is a special case of multicomponent diffusion. Multicomponent diffusion is diffusion in mixtures, and diffusiophoresis is the special case where we are interested in the movement of one species that is usually a colloidal particle, in a gradient of a much smaller species, such as dissolved salt such as sodium chloride in water. or a miscible liquid, such as ethanol in water. Thus diffusiophoresis always occurs in a mixture, typically a three-component mixture of water, salt and a colloidal species, and we are interested in the cross-interaction between the salt and the colloidal particle.
  It is the very large difference in size between the colloidal particle, which may be 1μm across, and the size of the ions or molecules, which are less than 1 nm across, that makes diffusiophoresis closely related to diffusioosomosis at a flat surface. In both cases the forces that drive the motion are largely localised to the interfacial region, which is a few molecules across and so typically of order a nanometer across. Over distances of order a nanometer, there is little difference between the surface of a colloidal particle 1 μm across, and a flat surface.
  Diffusioosmosis is flow of a fluid at a solid surface, or in other words, flow at a solid/fluid interface. The Marangoni effect is flow at a fluid/fluid interface. So the two phenomena are analogous with the difference being that in diffusioosmosis one of the phases is a solid. Both diffusioosmosis and the Marangoni effect are driven by gradients in the interfacial free energy, i.e., in both cases the induced velocities are zero if the interfacial free energy is uniform in space, and in both cases if there are gradients the velocities are directed along the direction of increasing interfacial free energy.